The objective of the work is to determine the thermal expansion coefficients of crystals using the method proposed by prof. E. S. Fedorov. The principle of the method is as follows: a plate is cut out of the crystal along the required plane and on one side of it, in one way or another, a diffraction grating is applied, the lines of which are perpendicular to the direction in which it is desirable to determine the expansion coefficient. If a beam of monochromatic light is passed through such a grating normal to the surface, then a series of deflected rays will be obtained, the angles of which with the normal obey the following law (see article).
